New developments in immunosuppressive therapy in renal transplantation

Primer on renal transplantation

Renal transplantation transforms chronically ill children with end stage renal disease (ESRD) into near normal resulting in improvement in nutrition, growth, neurodevelopment and quality of life, and is the goal of therapy. However, the benefits of transplantation come at a price of life-long treatment with immunosuppressive medications, increased risk of infections and malignancy. Children younger than 10 y of age have the best, and adolescents have the worst 5-y graft survival likely due to non-adherence with medications in the adolescents. Long-term complications include ongoing issues related to chronic kidney disease (CKD) and cardiovascular morbidity and mortality contributing to graft loss and shortened life expectancy, thus limiting the success of organ transplantation. Therefore, appropriate management of CKD and cardiovascular issues should be integral to the care of pediatric transplant patients. The other ongoing challenges include organ shortage, prevention and treatment of late acute rejections and chronic graft dysfunction, discovering reliable noninvasive immune monitoring tools, improving adherence, psychosocial rehabilitation, and the elusive goal of tolerance.

Gingival overgrowth in subjects under immunosuppressive regimens based on cyclosporine, tacrolimus, or sirolimus

AIM

To assess the prevalence and variables associated with gingival overgrowth (GO) in renal transplant recipients medicated with cyclosporine (CsA), tacrolimus (Tcr), or sirolimus (Sir).

MATERIALS AND METHODS

One hundred and thirty-five eligible subjects were divided in CsA, Tcr, and Sir groups comprising 45 subjects each. GO was visually assessed and subjects were assigned as GO+ or GO- in a post hoc definition. Saliva samples were collected and the presence of periodontal pathogens was assessed through polymerase chain reaction. Variables of interest were compared between GO+ and GO- subjects through univariate and multivariate analysis.

RESULTS

Prevalence of GO was of 60.0% for CsA, 28.9% for Tcr, and 15.6% for Sir groups. Within the CsA group, GO was associated with papillary bleeding index (p=0.001); within the Tcr group, GO was associated with CsA previous use (p=0.013), and calcium channel blockers (CCB) use (p=0.003); within the Sir group, GO was associated with papillary bleeding index (p=0.018), and CCB use (p=0.020). A higher frequency of Tannerella forsythia was observed among GO+ subjects medicated with Tcr.

CONCLUSION

Pharmacological and periodontal variables were associated with GO in different immunosuppressive regimens. Integration between the medical and the dental team may be an important approach in the post-transplant maintenance routine.

Targeting non-malignant disorders with tyrosine kinase inhibitors

Receptor and non-receptor tyrosine kinases are involved in multiple proliferative signalling pathways. Imatinib, one of the first tyrosine kinase inhibitors (TKIs) to be approved, revolutionized the treatment of chronic myelogenous leukaemia, and other TKIs with different spectra of kinase inhibition are used to treat renal cell carcinoma, non-small-cell lung cancer and colon cancer. Studies also support the potential use of TKIs as anti-proliferative agents in non-malignant disorders such as cardiac hypertrophy, and in benign-proliferative disorders including pulmonary hypertension, lung fibrosis, rheumatoid disorders, atherosclerosis, in-stent restenosis and glomerulonephritis. In this Review, we provide an overview of the most recent developments--both experimental as well as clinical--regarding the therapeutic potential of TKIs in non-malignant disorders.

Deficient TNF-alpha and IFN-gamma production correlates with nondetectable donor-specific cytotoxicity after clinical kidney transplantation

BACKGROUND

We previously reported that no cytotoxic T-lymphocyte precursor frequencies (CTLpf) were found in 60% of patients on azathioprine or mycophenolate mofetil+Pred long after kidney transplantation. We questioned whether the absence of donor-specific CTLpf was associated with low levels of stimulatory Th1 (tumor necrosis factor [TNF]-alpha, interferon [IFN]-gamma) or high levels of regulatory Th2 (interleukin [IL]-4, IL-6, IL-10) cytokines.

METHODS

In this study, peripheral blood monocyte cells (PBMC) were stimulated with irradiated donor cells. After 7 days, cytokine production was determined by cytokine bead array, and CTLpf by limiting dilution assay.

RESULTS

Patients with detectable CTLpf (> or =10/10(6) PBMC) had significantly higher levels of TNF-alpha (P=0.04) and IFN-gamma (P=0.02) than patients with nondetectable CTLpf (<10/10(6) PBMC). Donor-reactive IL-4, IL-6, and IL-10 production was comparable in both patient groups. Additionally, CTLpf was positively correlated with TNF-alpha (rs=0.54, P=0.0003) and IFN-gamma (rs=0.64, P<0.0001) production.

CONCLUSION

The absence of donor-specific CTLp after transplantation correlates with low levels of stimulatory cytokines, not with elevated levels of regulatory cytokines.

Short-term cyclosporine therapy and cotransplantation of donor splenocytes: effects on graft rejection and survival rates in pigs subjected to renal transplantation

BACKGROUND

Donor-specific allogeneic loading can prolong the survival of solid organ transplants by inducing a state known as acceptance. Several populations of cells are known to be involved in this process, but their exact roles have yet to be defined. The aim of this study was to assess the effects of portal-vein transfusion of donor-specific splenocytes (DST) after short-term cyclosporine A (CyA) therapy in pigs subjected to renal transplantation.

METHODS

Four groups of unrelated swine underwent renal transplantation with removal of the native kidneys. Antirejection protocols consisted in portal-vein DST (3 x 10(8) cells/kg) (Group 2, n = 7); intravenous CyA (9 mg/kg/d) on postoperative days 1-12 (Group 3, n = 14); and DST + CyA (as described above) (Group 4, n = 13). Results (through postoperative day 90) were compared with those obtained in untreated control recipients (Group 1, n = 7).

RESULTS

Compared with animals of Groups 1, 2, and 3, Group 4 recipients presented significantly longer survival (mean: 90 days, P < 0.01 in Kaplan-Meier analysis) and better renal function (P < 0.05). Graft histology revealed preserved parenchyma.

CONCLUSION

The role of spleen cells in the immune response has probably been underestimated. Cotransplantation of donor splenocytes seems to induce a certain degree of acceptance toward the renal allograft. The route of administration (portal-vein infusion in this study) may be crucial for developing favorable mechanisms of recognition.

Impact of Therapeutic Changes on Renal Graft Survival With Posttransplant Glomerulonephritis

INTRODUCTION

Posttransplant glomerulonephritis (GN) is the third cause of graft loss after 1 year of transplant follow-up; few approaches have been efficient in reversing this outcome. The aim of this study was to evaluate whether the modification of the immunosuppressive therapy for treating posttransplant GN had an impact on allograft survival.

PATIENTS AND METHODS

Forty-nine patients who underwent renal transplantation and developed posttransplant GN were divided into two groups: group 1, 22 patients with modified immunosuppressive treatment (72.3%, pulse of methylprednisolone; 13.6%, high-dose oral corticosteroid), and group 2, where it was maintained. Additionally, the impact of the concomitant use of drugs that promote the renin-angiotensin-aldosterone system blockade (RAASB) was analyzed in terms of graft survival.

RESULTS

We established the diagnosis of GN at 17.9 months (range, 0.57 to 153.4) after transplantation, when serum creatinine (Cr) was 2.2 mg/dL (range, 0.8 to 12.5) and proteinuria 3.2 g/L (range, 0.2 to 24.2). Graft survivals at 1 and 3 years after diagnosis were 69.2% and 52.9%, respectively. The patients of group 1 showed a lower prevalence of graft loss (27.2% versus 48.1%, P = .40) and better survival at the end of 1 year (73.2% versus 60.4%) and 3 years (62.5% versus 38.0%, P = .26), but the differences were not significant. RAASB showed a positive impact on survival at the end of 3 years in both groups: for group 1, 83.8% with RAASB, 41.4% without RAASB; and for group 2, 75% with RAASB and 14.8% without RAASB (P < .001).

CONCLUSION

Although treatment of posttransplant GN with modification of immunosuppression seemed to improve graft survival in the first 3 years after diagnosis, RAASB improved this effect.

Combined Use of the JAK3 Inhibitor CP-690,550 with Mycophenolate Mofetil to Prevent Kidney Allograft Rejection in Nonhuman Primates

BACKGROUND

Immunosuppression via Janus kinase (JAK) 3 inhibition affords significant prolongation of allograft survival. We investigated the effects of an immunosuppressive regimen combining the JAK3 inhibitor CP-690,550 with mycophenolate mofetil (MMF) in nonhuman primates (NHPs).

METHODS

Life-supporting kidney transplantations were performed between ABO-compatible, MLR-mismatched NHPs. Animals were treated orally twice a day with CP-690,550 and MMF (n=8) or MMF alone (n=2) and were euthanized at day 90 or earlier due to allograft rejection.

RESULTS

Mean survival time (+/-SEM) in animals treated with MMF alone (23+/-1 days) was significantly extended in animals that concurrently received CP-690,550 (59.5+/-9.8 days, P=0.02). Combination animals exposed to higher levels of CP-690,550 had a significantly better survival (75.2+/-8.7 days) than animals that received less CP-690,550 (33.3+/-12.6 days, P=0.02). Three combination therapy animals were euthanized at day 90 with a subnormal renal function and early-stage acute graft rejection. Rejection, delayed by treatment, ultimately developed in other animals. Anemia and gastrointestinal intolerance was seen in combination therapy animals that otherwise did not show evidence of viral or bacterial infection besides signs consistent with subclinical pyelonephritis (n=3). One incidental lymphosarcoma was noted.

CONCLUSIONS

Addition of CP-690,550 to MMF significantly improved allograft survival. The observed side effects appear amenable to improvements upon alteration of dosing strategies. Efficacy of this combination regimen suggests that it could become the backbone of calcineurin inhibitor-free regimens.

Effects of JAK3 Inhibition with CP-690,550 on Immune Cell Populations and Their Functions in Nonhuman Primate Recipients of Kidney Allografts

BACKGROUND

Janus Kinase (JAK) 3 is a tyrosine kinase essential for proper signal transduction downstream of selected cytokine receptors and for robust T-cell and natural killer cells activation and function. JAK3 inhibition with CP-690,550 prevents acute allograft rejection. To provide further insight into the mechanisms of efficacy, we investigated the immunomodulatory effects of CP-690,550 in vitro and in vivo in nonhuman primates.

METHODS

Pharmacodynamic assessments of lymphocyte activation, function, proliferation and phenotype were performed in three settings: in vitro in whole blood isolated from untransplanted cynomolgus monkeys (cynos), in vivo in blood from untransplanted cynos dosed with CP-690,550 for 8 days, and in vivo in blood from transplanted cynos immunosuppressed with CP-690,550. Cell surface activation markers expression, IL-2- enhanced IFN-gamma production, lymphocyte proliferation and immune cell phenotype analyzes were performed with multiparametric flow cytometry.

RESULTS

In vitro exposure to CP-690,550 resulted in significant reduction of IL-2-enhanced IFN-gamma production by T-cells (maximum inhibition of 55-63%), T-cell surface expression of CD25 (50% inhibitory concentration (IC50); 0.18 microM) and CD71 (IC50; 1.6 microM), and T-cell proliferative capacities measured by proliferating cell nuclear antigen expression (IC50; 0.87 microM). Similar results were observed in animals dosed with CP-690,550. In addition, transplanted animals displayed significant reduction of NK cell (90% from baseline) and T-cell numbers whereas CD8 effector memory T-cell populations were unaffected.

CONCLUSIONS

Potent in vitro and in vivo immunomodulatory effects of the JAK3 inhibitor CP-690,550 likely contribute to its efficacy in the prevention of organ allograft rejection.

Calcineurin Inhibitor Withdrawal in Stable Kidney Transplant Patients Decreases the Donor-Specific Cytotoxic T Lymphocyte Precursor Frequency

BACKGROUND

In a prospective study, calcineurin inhibitors (CNI) were withdrawn in patients two years after kidney transplantation. We questioned whether stopping CNI had an effect on the donor-specific reactivity, as CNI might hinder immune responses leading to graft acceptance.

METHODS

We measured the donor-specific cytotoxic T lymphocyte (CTL) precursor frequency (CTLpf) in 54 patients before and after withdrawal of CNI. In addition, the T-cell reactivity of PBMC to donor and third-party antigens was tested in MLR, and in IFNgamma-Elispot. Reactivity to tetanus toxoid (TET) was studied as well.

RESULTS

Donor-specific CTLpf significantly decreased after CNI withdrawal (P=0.0001). In contrast, no difference was observed in third-party reactive CTLpf, donor and third-party reactive MLR and IFNgamma-Elispot. Proliferative responses and the number of IFNgamma-producing cells to TET also decreased after CNI withdrawal. The decrease in CTLpf correlated with the time between the two blood samples (before and after stopping CNI, P=0.05). This decrease was caused by stopping CNI, because there was no correlation between CTLpf and the duration of the CNI treatment after transplantation. Moreover, the percentage of regulatory T cells in the peripheral blood increased after CNI withdrawal.

CONCLUSIONS

We report here that after withdrawal of CNI the donor-specific CTLpf decreases. We hypothesize that CNI suppress regulatory mechanisms that have the potential to down-regulate donor-specific CTL responses and reactivity to TET.

Renal transplantation: the present and the future

Children receiving kidney transplants in the modern era in developed countries have excellent overall results. Graft survival and patient survival in children is now virtually equal to that in adult organ recipients. Deceased donor source kidneys are no longer associated with significantly inferior outcomes. These advances are in large part due to development in more potent immunosuppressive agents and newer combinations. These advances have also come at a price in the form of increased post-transplant infections. The transplant community is now moving to minimization protocols to reduce the adverse effects of many of the medications and to reduce the incidence of infections. Newer techniques of diagnosis of acute rejection, degree of immunosuppression and DNA-based viral surveillance are changing the face of clinical practice. Newer technologies such as stem cell transplantation, tissue engineering and xenotransplantation promise even more changes in the future.

A combination of anergic cells' adoptive transfer and rapamycin therapy prolongs cardiac allograft survival in mice

The in vivo immunoregulatory effect of anergic cells induced by blocking the costimulatory pathway was investigated in this study. Anergic cells were generated in vitro by mixed culture of murine splenic cells from BALB/c and C3H/HeJ under the blockade of anti-CD154 and anti-CD80 monoclonal antibodies, and the in vitro activity of anergic cells were observed. The 3.0 Gy gamma-irradiated BALB/c mice received cardic allografts from C3H/HeJ, and anergic cells were intravenously injected immediately after transplantation. Recipient mice injected with anergic cells also received rapamycin therapy (1 mg/kg/day) for 14 days. On day 7 after transplantation, the subsets of peripheral blood T lymphocytes, the pathology of grafts and the infiltration of lymphocytes in grafts were analysed. Untreated gamma-irradiated animals showed a graft median survival time (MST) of 9 days. Animals injected with anergic cells only or receiving rapamycin therapy alone showed MST of 11 and 17 days, respectively. MST of allograft in mice treated with control cells plus rapamycin therapy was 9 days. Animals injected with anergic cells plus rapamycin therapy, but receiving third-party allografts (C57BL/6J), showed an MST of 15 days. However, anergic cell injection plus rapamycin therapy prolonged allograft survival significantly (MST 28 days, P < 0.01). The rejection was mild and tissue architecture was preserved in recipient mice receiving anergic cell injection plus rapamycin therapy. Furthermore, anergic cells and rapamycin therapy decreased the percentage of peripheral blood CD4+ and CD8+ T cells (including CD25+, CD152+, CD154+ and CD28+ subsets) and greatly reduced the infiltrating lymphocytes in allografts (including CD3+, CD4+, CD8+ and CD25+ T cells). In conclusion, the treatment based on anergic cells' adoptive transfer plus rapamycin therapy demonstrated a significant prolongation of murine cardiac allograft survival in a donor antigen-specific manner. This therapeutic protocol alleviated allograft rejection to solid allograft in vivo.

Immunosuppression by the JAK3 Inhibitor CP-690,550 Delays Rejection and Significantly Prolongs Kidney Allograft Survival in Nonhuman Primates

BACKGROUND

Janus kinase 3 (JAK3) mediates signal transduction from cytokine receptors using the common chain (gammac). Because mutations in genes encoding gammac or JAK3 result in immunodeficiency, we investigated the potential of a rationally designed inhibitor of JAK3, CP-690,550, to prevent renal allograft rejection in nonhuman primates.

METHODS

Life-supporting kidney transplantations were performed between mixed leukocyte reaction-mismatched, ABO blood group-matched cynomolgus monkeys. Animals were treated with CP-690,550 (n = 18) or its vehicle (controls, n = 3) and were euthanized at day 90 or earlier if there was allograft rejection.

RESULTS

Mean survival time (+/- standard error of mean) in animals treated with CP-690,550 (53 +/- 7 days) was significantly longer than in control animals (7 +/- 1 days, P=0.0003) and was positively correlated with exposure to the drug (r = 0.79, P < 0.01). Four treated animals were euthanized at 90 days with a normal renal function and low-grade rejection at final pathology. Occurrence of rejection was significantly delayed in treated animals (46 +/- 7 days from transplantation vs. 7 +/- 1 days in controls, P = 0.0003). Persistent anemia, polyoma virus-like nephritis (n = 2), and urinary calcium carbonate accretions (n = 3) were seen in animals with high exposure. Natural killer cell and CD4 and CD8 T-cell numbers were significantly reduced in treated animals. Blood glucose, serum lipid levels, and arterial blood pressure were within normal range in treated animals, and no cancers were demonstrated.

CONCLUSIONS

CP-690,550 is the first reported JAK3 inhibitor combining efficacy and good tolerability in a preclinical model of allotransplantation in nonhuman primates and thus has interesting potential for immunosuppression in humans.

Synthesis, stereochemical determination and biochemical characterization of the enantiomeric phosphate esters of the novel immunosuppressive agent FTY720

The novel immunosuppressive agent FTY720 (1) is phosphorylated in vivo in a variety of species yielding an active metabolite that is an agonist of four of the five known G-protein-coupled sphingosine-1-phosphate (S1P) receptors. A synthesis amenable to producing gram quantities of the stereoisomeric phosphate esters, a determination of their absolute stereochemistry via an enantioselective synthesis and their characterization as S1P receptor agonists and antagonists is reported.

Rejection of human islets and human HLA-A2.1 transgenic mouse islets by alloreactive human lymphocytes in immunodeficient NOD-scid and NOD-Rag1nullPrf1null mice

Immunodeficient NOD mice engrafted with human peripheral blood mononuclear cells (PBMCs) were used in two models of human islet allograft rejection. Model one: human PBMCs were engrafted into chemically diabetic NOD-scid mice bearing established subrenal human islet allografts. Inflammation and often complete islet allograft rejection were observed. Model 2 incorporated three key advances. First, we developed a new immunodeficient recipient, NOD-RagI(null)Prf1(null) mice. Second, graft-lymphocyte interactions were optimized by intrasplenic co-transplantation of islets and human PBMC. Third, NOD-scid islets expressing human HLA-A2.1 were used as allograft targets. Diabetic NOD-RagI(null)Prf1(null) recipients of HLA-A2.1 transgenic mouse islets, alone or co-engrafted with HLA-A2-positive human PBMC, exhibited durable graft survival and euglycemia. Contrastingly, co-transplantation with HLA-A2-negative human PBMC led to islet graft rejection without evidence of graft-vs.-host disease (GVHD). We propose that diabetic NOD-RagI(null)Prf1(null) mice co-engrafted with HLA-A2 mouse transgenic islets and allogeneic human PBMC provide an effective in vivo model of human islet allograft rejection.

New concepts in organ transplantation

Over the past several decades, many factors have led to higher rates of patient and graft survival in organ transplantation. These factors include enhanced immunosuppressants available in recent years such as Neoral, Prograf, sirolimus, mycophenolate mofetil and anti-interleukin-2 receptor monoclonal antibodies. In addition, other new drugs, such as FTY 720, FK 778, anti-CD20, anti-CD40, and anti-CH52 monoclonal antibodies, are now being tested in clinical studies. Furthermore, there have been advances in surgical techniques, such as the piggyback method without venovenous bypass, side-to-side anastomosis of the hepatic veins, use of vascular staplers, biliary duct-to-duct anastomosis with or without tube drainage, microsurgical hepatic artery anastomosis and laparoscopic donor nephrectomy. Finally, better patient and donor selection criteria with regard to HBV- and HCV-seropositive donors, diabetic donors, donors with malignancies, older donors, ABO-incompatible donors, and non-heart-beating donors have been combined with optimal timing of transplantation, better options for treating early surgical and late medical complications, and improved management in intensive-care units. Other noteworthy scientific and social development are on the horizon namely genetic advances in xenografting and cell transplantation, and induction of immunologic tolerance. This article reviews the current developments that have significantly improved graft and patient survival among solid-organ transplants.

Histologic features in primary cutaneous squamous cell carcinomas in immunocompromised patients focusing on organ transplant patients

BACKGROUND

In organ transplant recipients (OTR) there is an increased incidence of cutaneous squamous cell carcinomas (CSCC), and they may be aggressive.

OBJECTIVE

We wanted to determine whether any histologic features were characteristic or more common in CSCC of OTR.

METHODS

A total of 518 immunocompetent individuals with 601 primary CSCC were examined. Seventy-nine OTR with 231 primary CSCC, 53 renal OTR, 25 heart/heart lung OTR, and 1 liver OTR were examined.

RESULTS

In all patient populations, CSCC occurred dominantly in chronically sun-exposed skin. In OTR, however, a greater percentage occurred on the extremity, particularly the upper extremity, and they occurred at an earlier age. Features that were significantly more common in OTR were acantholytic changes, early dermal invasion, an infiltrative growth pattern with or without desmoplasia, and Bowen's disease with carcinoma. In OTR primary CSCC were also significantly deeper at time of diagnosis.

CONCLUSIONS

Our findings confirmed the association of ultraviolet radiation exposure with development of CSCC in OTR. The increased depth of the primary CSCC in OTR is surprising because these patients are followed closely for skin cancer compared with immunocompetent patients. The other morphologic features that were significantly more common in OTR may theoretically reflect not only the type of iatrogenic immunosuppression in these patients, but also other procarcinogenic effects of their medications.

Alloreactive CD4+ and CD8+ T cells express the immunotolerant HLA-G molecule in mixed lymphocyte reactions: in vivo implications in transplanted patients

HLA-G displays immunotolerogenic properties towards the main effector cells involved in graft rejection through inhibition of NK- and CTL-mediated cytolysis and CD4+ T cell alloproliferation. HLA-G expression is restricted in healthy tissues to trophoblast and thymus but is extended to various tissues under pathological conditions. HLA-G was detected in allograft biopsies and sera from transplanted patients who displayed a better graft acceptance. However, the cells involved in such de novo expression of HLA-G remain to be characterized. By flow cytometry and confocal microscopy, we demonstrated that, following allogeneic stimulation in vitro, both CD4+ and CD8+ T cell subsets can express membrane-bound HLA-G1 and/or soluble HLA-G5 molecules. Such HLA-G1/-G5 expression is regulated at the transcriptional level. Soluble HLA-G5 could be detected by using a novel monoclonal antibody, 5A6G7, specific for the intron 4-retaining sequence of HLA-G5. Finally, the biological relevance of these data was provided by analysis of transplanted patients in whom we identified both CD4+ and CD8+ T cells expressing HLA-G. The HLA-G-positive T cells we describe here may constitute a cellular source of HLA-G after allotransplantation and may be involved in the improved graft acceptance which is observed in HLA-G-positive transplanted patients.

Alloimmune injury and rejection of human skin grafts on human peripheral blood lymphocyte-reconstituted non-obese diabetic severe combined immunodeficient beta2-microglobulin-null mice

Small animal models with the capacity to support engraftment of a functional human immune system are needed to facilitate studies of human alloimmunity. In the present investigation, non-obese diabetic (NOD) severe combined immunodeficient (scid) beta2-microglobulin-null (B2mnull) mice engrafted with human peripheral blood lymphocytes (hu-PBL-NOD-scid B2mnull mice) were used as in vivo models for studying human skin allograft rejection. Hu-PBL-NOD-scid B2mnull mice were established by injection of human spleen cells or PBLs and transplanted with full-thickness allogeneic human skin. Human cell engraftment was enhanced by injection of anti-mouse CD122 antibody. The respective contributions of human CD4+ and CD8+ cells in allograft rejection were determined using depleting antibodies. Human skin grafts on unmanipulated NOD-scid B2mnull mice uniformly survived but on chimeric hu-PBL-NOD-scid B2mnull mice exhibited severe immune-mediated injury that often progressed to complete rejection. The alloaggressive hu-PBLs did not require prior in vitro sensitization to elicit targeted effector cell activity. Extensive mononuclear cell infiltration directed towards human-origin endothelium was associated with thrombosis and fibrin necrosis. No evidence of graft-versus-host disease was detected. Either CD4+ or CD8+ T cells may mediate injury and alloimmune rejection of human skin grafts on hu-PBL-NOD-scid B2mnull mice. It is proposed that Hu-PBL-NOD-scid B2mnull mice engrafted with human skin will provide a useful model for analysis of interventions designed to modulate human allograft rejection.

Renal transplantation

Renal transplantation offers the best renal replacement therapy for most children with end stage renal disease improving their potential for growth and nutrition, neurodevelopment and quality of life. Advances in organ retrieval and preservation, improved surgical techniques, newer immunosuppressive drugs and prevention and treatment of infections have significantly improved patient and graft survival. The absolute requirements for a transplant are compatible blood group and a negative cytotoxic crossmatch. The immunosuppressive drugs most often used are cyclosporin A (or tacrolimus), azathioprine (or mycophenolate mofetil) and prednisone. Complications following transplantation include episodes of acute rejection, serious bacterial and viral infections, hypertension and recurrence of primary disease in the allograft. Each centre must have standard protocols for pre-transplant evaluation, management of immunosuppression and prevention of infections. Socio-economic factors should be carefully evaluated before offering transplantation to children in developing countries. Preemptive transplantation from a living donor may be a more viable option for these children.

The complementary roles of deletion and regulation in transplantation tolerance

Neonatal tolerance of alloantigens was described in mice nearly half a century ago, but unfortunately, the translation of these early findings into the clinical arena proved to be much more challenging than was first anticipated. However, the past decade has seen considerable progress in our understanding of the mechanisms that contribute to transplantation tolerance in experimental models. This review outlines our current understanding of the mechanisms of allograft tolerance, emphasizing the complementary roles of deletion and regulation of alloreactive T cells.

Stem cell medicine encounters the immune system

Recent progress in deriving human embryonic stem (hES) cells and defining their capacity to differentiate has inspired hope that they could become a source of replacement cells for damaged or diseased tissues. We review the immunological barriers to transplanting hES cells and consider several potential solutions, including stem-cell banking, modification of the immunogenicity of donor cells and induction of tolerance to the graft. We evaluate the probable efficacy of these approaches with a view to facilitating the use of hES cells in clinical practice.